Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 122057
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
357 PM CDT Thu Apr 12 2018

.SHORT TERM...(This evening through Friday)
Issued at 345 PM CDT Thu Apr 12 2018

Over the next 24 hours conditions in terms of wind, precipitation
and impacts will increase significantly. A variety of weather is
also expected with isolated severe hail along the Iowa border late
tonight /Friday afternoon, to blizzard conditions in west
central/southwest Minnesota by Friday evening.

Precipitation will develop after midnight along the Iowa border,
and slowly spread northward on Friday. Most of the precipitation
will be in the form of rain. Some thunderstorms are also likely in
far southern Minnesota after midnight. The precipitation will
slowly spread across the rest of southern and central Minnesota by
Friday afternoon, and again, mainly in the form of rain.

.LONG TERM...(Friday night through Thursday)
Issued at 350 PM CDT Thu Apr 12 2018

...POWERFUL STORM AND HIGH SNOWFALL AMOUNTS BECOMING LIKELY...

First, the storm system in question that will bring significant
impacts to the Upper Midwest was across the Rockies/Great Basin.
This system is very dynamic with several short waves embedded in the
long wave trough moving across the western CONUS. A very sharp air
mass change is evident in the Central Plains with 70s/80s in
Missouri, to the 40s/50s in Minnesota. The dividing line was along
the Missouri/Iowa border where winds shift from the south, to the
east/northeast. Wind energy is also very apparent with strong
west/southwest winds across the Rockies, and into the Plains which
will create a very pronounce line of where Winter remains, to an
outbreak of severe storms.

Secondly, confidence is high that snow will develop across west
central/southwest Minnesota late Friday afternoon/evening, and
slowly spreading northeast across the rest of southern
Minnesota/west central Wisconsin Friday night/Saturday. Lower
confidence remains on the onset of heavier snowfall across far
southern Minnesota where the thermal profile is more critical in
terms of freezing temperatures which will take longer to cool.
There has also been a slight shift southward of the precipitation
field on both the EC/GEM. The GFS has been consistently further to
the north with the heavier bands in central Minnesota, vs the
GEM/EC. However, even the GEM/EC shows snow developing across
southern/eastern Minnesota by Saturday afternoon/evening as the
system begins to pivot to the east/northeast and strengthens some.

Thirdly, this could be two separate systems, with one impacting west
central/southwest Minnesota Friday afternoon/evening with the
heaviest snowfall and highest sustained winds. Further to the east,
it will be mainly rain, mixed with snow/sleet until late Friday
evening where the turn over could be even later. There could also be
a lull in the precipitation Friday afternoon/evening is more
convection develops in northern Iowa and shifts this energy off to
the northeast across southern Wisconsin. This is what both the
EC/GEM are indicating initially, with the GFS more broad brushing
the precipitation across all of the Upper Midwest. The second part
of this system will be associated with the main upper wave moving
across the Central Plains Saturday, into Saturday night. The EC/GEM
and the GFS all support a secondary /deformation type zone/ across
southern/east central Minnesota Saturday afternoon/evening. The main
concern is the possibility of a lull in the precipitation and people
begin to start traveling, and then the next wave moves across the
region and develops a secondary area of heavy snow.

This is a very complicated system, large, and has a few
uncertainties to create havoc in the forecast. Thus, with the
highest confidence, we are going to issue a blizzard warning for
portions of west central and southwest Minnesota starting Friday
evening. This is where both strong sustained winds and high snowfall
totals occur. Further to the north, south and east, uncertainties
exists on a mixture of sleet and ice, and further how much of the
drier air to the north, holds on amounts in central Minnesota.

In addition to the winter precipitation, the strength of this system
to the south of Minnesota with significant elevated CAPE and wind
energy, could be enough to generate a few severe storms. The main
threat will be across Iowa. However, lower freezing levels in
southern Minnesota, combined with the elevated CAPE/Lapse Rates, I
wouldn`t be surprised to see an isolated severe hail stone along the
Iowa border. Plus, Friday afternoon could be a concern if the
surface boundary moves further to the north and an area of storms
develops across far southern Minnesota.

As discussed before, the secondary system over the weekend could
linger the snowfall into Sunday with additional accumulations
possible. Once this system moves out, a couple of days of dry
weather is expected. However, this active weather will continue with
another Spring storm possible by Wednesday/Thursday. Temperatures
will also remain below average through at least the third week of
April.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1205 PM CDT Thu Apr 12 2018

Two areas of MVFR cigs will slowly erode during the afternoon
around KRNH/KEAU and in far southwest Minnesota near KRWF.
Elsewhere, VFR conditions will prevail with a northeast wind
slowly increasing in speed.

Between 00-06z, bands of showers will develop in Iowa and move
northward into far southern Minnesota. After 6z, conditions will
deteriorate in southern Minnesota, and spread northward during the
morning. Bands of rain, moderate to heavy at times, are likely. A
few isolated TSRA are also possible, but mainly confined to
northern Iowa. Later TAFs could introduce TSRA, other than KMKT
with VCTS after 6z. After 12z, conditions will likely drop to IFR
with gusty northeast winds of 15-25 kts, with occasional gusts of
30-35 kts in southwest Minnesota.

KMSP...

As discussed above, the worst conditions will occur after 12z,
with a period of rain in the morning, and afternoon. Some PL is
possible during the afternoon but confidence is low. A light
north-northeast wind this afternoon with strengthen and become
gusty overnight.

/OUTLOOK FOR KMSP/

Fri Evening... RA bcmg SN/PL small chc of FZRA. Wind NE 20G35kts.
Sat...IFR or LIFR - SN/PL turning to SN. Several inches likely.
Wind NE 20g35 kts.
Sun...IFR/MVFR with lingering snow. Wind N at 15G20kts.


&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Watch from late Friday night through late Saturday
     night for WIZ024-026-028.

     Winter Storm Watch from Friday evening through late Saturday
     night for WIZ023-025-027.

     Winter Storm Watch from Friday evening through late Saturday
     night for WIZ014>016.

MN...Winter Storm Watch from late Friday night through late Saturday
     night for MNZ076>078-083>085-091>093.

     Winter Storm Watch from Friday afternoon through late Saturday
     night for MNZ041>045-047>050.

     Winter Storm Watch from Friday evening through late Saturday
     night for MNZ060-062-063-066>070-074-075-082.

     Winter Storm Watch from Friday evening through late Saturday
     night for MNZ051>053-058-059-061.

     Blizzard Warning from 7 PM Friday to 1 AM CDT Sunday for
     MNZ054>057-064-065-073.

&&

$$

SHORT TERM...JLT
LONG TERM...JLT
AVIATION...JLT



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